Leaf structure and why it matters


Leaves exchange gases via stomata



CO2 IN, O2 and H2O OUT

How stomata work…



* CO2 enters leaf and then chloroplasts through concentration gradient
* Stomata not always open….WHY???

Leaf gas exchange impacts the global atmopshere


Vascular tissues in leaves are confined to veins



  • Transpiration is a by‐product of opening stomatal pores

  • H2O transport needs to be sufficient to keep stomata open

  • Venation represents investment in H2O supply

Angiosperms have evolved higher vein densities


  • Helps explain angiosperm dominance
  • Transpiration alters global climate systems!

Leaf economic theory: Return on Investment


Photosynthesis is complicated….



What do plants do when they are hungry?


Photosynthesis is the basis for most life on Earth





  • Greek = “building with light”
  • Autotroph = “self nourishing”
  • Photoautotroph = “self nourishing with light”


  • Photosynthesis is an energy pathway
    • 2 linked reactions
    • light reaction + Calvin cycle

Chloroplasts: Where the magic happens


The nature of light



When light hits chlorophyll a few things can happen


When pigments absorb photons an election gets excited


Photosystems (2) convert light energy to chemical energy


Light reactions: make ATP + NADPH for Calvin cycle



Calvin cycle occurs in the stroma


Calvin cycle is a 3-step process



  • 1. Fixation: CO2 reacts with 5C molecule (RUBP)
    • new 6C split into 2 acids (3C each)
    • catalyzed by Rubisco enzyme


  • 2. Reduction: ATP and NADPH turn 3C acids into sugars
    • reduction of acids


  • 3. Regeneration: Some 3C sugars recycled to make RUBP (5C)
    • one 3C sugar leaves to make carboydrates/sugars
    • recycling also needs ATP

Making sugars requires several cycles